If you meant that the first partition was a boot partition (with a mount point of "/boot") and that the third partition was for both root and home (with mount point of "/"), then you will need to adjust what wayne128 has already posted to fit that scenario. Try the commands he suggested first. If they don't work, then boot again using live LMDE disk and do the following in a terminal:

If you don't see something like that, then the sde1 partition is likely just your /boot partition. You will need to mount both the /boot partition and the /root partition; then run the grub install commands. Assuming that is what you need to do, continue on with the following in a terminal:

(NOTE: if you get a message after trying to mount /dev/sda1 to /mnt/boot that there is no such directory, create the directory by entering sudo mkdir /mnt/boot, then run that mount command again followed by the grub-install command.)

P.s.A separate boot partition is not really necessary and does not need to be anywhere close to 20GB in size if you do decide to use one. Swap partition doesn't need to be any bigger than 8-9GB on your system. If you decide to start over at some point in the future, you may want to consider changing the way system is partitioned. For now, once you get booting straightened out, you'll be fine as it is. Just bringing this up for future reference and consideration.

Please add [SOLVED] to your thread if a solution is found. Go to your first post in the thread, hit "Edit" button and add [SOLVED] to the title of the post.